> I'm having a hard time explaining how to disable a hidden item for one user in Startup Applications?

why do you need to disable system services this way? Could you give examples? Those autostarts are often conditional to a gsettings or a configuration option and the natural place to disable the service should be in the corresponding config dialog and not to have to workaround by editing autostart launchers

2) Guest accounts or dedicated accounts. For example, I use a dedicated account to play music. It's a restricted account with no password, everyone can use it to play music. This account shall never
- log into Ubuntu One or even try to (ubuntuone-launch.desktop)
- display update notifications (update-notifier.desktop)
- search for drivers (jockey-gtk.desktop)
- do any social networking (gwibber.desktop, telepathy-indicator.desktop)

Right, it will be off by default next cycle and a checkbox to turn it on or off will be added to the sound configuration dialog which is the dialog most user look for a such setting

> 2) Guest accounts or dedicated accounts. For example, I use a dedicated account to play music. It's a restricted account with no password, everyone can use it to play music. This account shall never
> - log into Ubuntu One or even try to (ubuntuone-launch.desktop)
> - display update notifications (update-notifier.desktop)
> - search for drivers (jockey-gtk.desktop)
>- do any social networking (gwibber.desktop, telepathy-indicator.desktop)

The guest accounts example don't work, the user directory for those is recreated at each session....
We are not saying that there is no usecase to disable services, but services should be configuration where it makes sense (the ubuntuone-control-panel for u1, jockey starts only once if your configuration doesn't change, im clients don't do anything if you don't have any account configuration, update-notifier can be tweaked from dconf-editor)